1. Field of the Invention
The present invention relates to a method for forming graphene nanoribbons.
2. Description of the Related Art
As technology progresses, different novel materials and structures, for example, fullerene, carbon nanotube, graphene, and graphene nanoribbon have been developed to meet the requirements of miniaturization of the elements or devices due to their special crystallinity and conductivity.
The graphene nanoribbon is currently the thinnest but hardest nano-material in the world. The graphene nanoribbon is a two-dimensional material that comprises a plurality of sp2-hybridized carbon atoms interconnected to form a one-atom thick sheet having a honeycomb crystal lattice. The graphene nanoribbon is almost completely transparent, and has a thermal conductivity coefficient of 5300 W/m·K that is higher than those of the carbon nanotube and diamond. Further, the graphene nanoribbon has a relatively high electron mobility at room temperature, i.e., about 15000 cm2/V·s, that is higher than those of copper and silver, and has a relatively low resistivity, i.e., about 10−6 Ω·cm, that is lower than that of copper or silver. Therefore, it is expected that the graphene nanoribbon can be used to develop new electronic components or transistors that are thinner and have high electrical transmission speed, or can be used to manufacture transparent touchscreens, liquid crystal displays, or even solar cells.
Nowadays, graphenenanoribbons have been fabricated by scanning tunneling microscope lithography and chemical vapor deposition. In addition to the above-mentioned methods, carbon nanotubes have been more recently utilized as the starting material to obtain graphene nanoribbons. In the prior literatures, many processes to prepare graphene nanoribbons from carbon nanotubes are disclosed, and include wet chemical methods, physicochemical methods, intercalation-exfoliation, catalytic approaches, electrical methods, sonochemical methods, and electrochemical methods. Kosykin et al (Nature, Vol. 458, p. 872-876, Apr. 16, 2009) disclosed a carbon nanotube-unzipping process that involves treating a carbon nanotube with concentrated sulphuric acid, followed by treating with potassium permanganate as a strong oxidant, and heating at 55-70° C. in a heat convection manner. This process chemically unzips the carbon nanotube to form nanoribbons. However, in this method, the step of heating the carbon nanotube at 55-70° C. has to last for at least two hours in order to achieve a proper condition to unzip the carbon nanotube. Therefore, this method is time-consuming and energy-consuming. In addition, because the heating step lasts for at least two hours, the structure of the carbon nanotube is likely to be destroyed, thereby resulting in low yield and inferior quality of the graphene nanoribbons.